Barometric Draft questions

[fields_mj]

I'm currently in the process of researching my next wood furnace. I'm currently using an add on unit that was built in 1980 and is quickly reaching the end of its life. Over the past several years, I've seen various posts on various forums about Kuma's VF100 and I've noticed they often mention the use of a barometric draft. From what I gather, a barometric draft limits the amount of draft the appliance can generate. When the chimney is cold and the fire is out, a barometric draft would be completely closed. As the appliance and chimney heat up and start drawing more draft, the barometric draft opens and pulls in room temperature air to control/limit the amount of draft being generated. Is this correct?

If this is the way a barometric draft works, I'm guessing that its purpose is to help keep the unit from burning too fast. I presume that using a barometric draft with an older appliance (ie non-gasification) can be problematic because it can cool the exhaust gas to the point that creosote could build up faster in the chimney. With the gasification units, I'm guessing that this is less of an issue because most of the exhaust gasses are burned in the gasification process. Does this all sound right, or am I off base with something?

 

[sloeffle]

I'm currently in the process of researching my next wood furnace. I'm currently using an add on unit that was built in 1980 and is quickly reaching the end of its life. Over the past several years, I've seen various posts on various forums about Kuma's VF100 and I've noticed they often mention the use of a barometric draft. From what I gather, a barometric draft limits the amount of draft the appliance can generate. When the chimney is cold and the fire is out, a barometric draft would be completely closed. As the appliance and chimney heat up and start drawing more draft, the barometric draft opens and pulls in room temperature air to control/limit the amount of draft being generated. Is this correct?

Yes

If this is the way a barometric draft works, I'm guessing that its purpose is to help keep the unit from burning too fast. I presume that using a barometric draft with an older appliance (ie non-gasification) can be problematic because it can cool the exhaust gas to the point that creosote could build up faster in the chimney. With the gasification units, I'm guessing that this is less of an issue because most of the exhaust gasses are burned in the gasification process. Does this all sound right, or am I off base with something?

Spot on. A forced draft unit will not have a barometric damper. My gasification OWB is forced draft, and I don't have a barometric damper. The chimney is the "engine" on a natural draft gasifier, stove, or furnace where the fan is on a forced draft boiler, furnace, or stove.

Not to split hairs, but I don't think a Kuuma wood furnace is a true gasification unit. I think they've just engineered and built a really good system to burn the wood gas. Someone please correct me if I'm wrong.

 

[brenndatomu]

Spot on. A forced draft unit will not have a barometric damper. My gasification OWB is forced draft, and I don't have a barometric damper. The chimney is the "engine" on a natural draft gasifier, stove, or furnace where the fan is on a forced draft boiler, furnace, or stove.

Not to split hairs, but I don't think a Kuuma wood furnace is a true gasification unit. I think they've just engineered and built a really good system to burn the wood gas. Someone please correct me if I'm wrong

I had a forced draft Yukon that they recommended a baro on. (recommended draft was only -0.03"WC!)
And they (Lamppa) classify the VF as an "updraft gasifier"

From what I gather, a barometric draft limits the amount of draft the appliance can generate.

The baro regulates the chimney draft...the waste heat from the burner rising in the chimney (hot air rising into colder air) is what generates the draft (one more reason that its important that your chimney be right) the draft being too high makes the appliance burn too hot and makes it more inefficient because the hot exhaust gasses race through the furnace too fast to properly be absorbed/exchanged by the furnace heat exchanger surface.
Modern stoves/wood furnaces are much more efficient and waste a lot less heat up the chimney, so a chimney that was fine for 39 years running grampas old forest eater, may not work worth diddly on a modern efficient wood burner.
I love the control that using a baro gives you, but would not want to run one on an oversized and/or uninsulated chimney, and not on a burner that was not a modern clean burner (burning DRY wood!)
Theres a lot of misinformation out there on barometric dampers...people think they are the boogeyman, but I guarantee that Daryl Lamppa would send you one with his furnace if it was a bad idea!

 

[brenndatomu]

but I guarantee that Daryl Lamppa would send you one with his furnace if it was a bad idea!

Too late to edit, but that was supposed to be would not

 

[salecker]

Yes


Spot on. A forced draft unit will not have a barometric damper. My gasification OWB is forced draft, and I don't have a barometric damper. The chimney is the "engine" on a natural draft gasifier, stove, or furnace where the fan is on a forced draft boiler, furnace, or stove.

Not to split hairs, but I don't think a Kuuma wood furnace is a true gasification unit. I think they've just engineered and built a really good system to burn the wood gas. Someone please correct me if I'm wrong.

I have a barometric on my gasification boiler

 

[sloeffle]

I have a barometric on my gasification boiler

I had a forced draft Yukon that they recommended a baro on. (recommended draft was only -0.03"WC!)
And they (Lamppa) classify the VF as an "updraft gasifier"

Interesting, guess I've learned something.

 

[PassionForFire&Water]

Video of ideal barometric damper
- adjustable
- sealed
- explosion relief (for cordwood gasifiers)

 

[salecker]

That one looks way better than the one i am using
the explosion relief would be a great feature as i have to fix mine every few months as it gets slammed from explosions that bend the stop which causes to much movement which causes the pins to come out of the hinges.